Field of the Invention
The present invention relates to a robot hand controlling method and a robotics device that control a robot hand.
Description of the Related Art
In recent years, a robotics device including a robot hand is used as an industrial robot to advance the automation of product assembly conventionally performed by manpower. When the robot hand is used to handle a work to assemble a variety of products, the work needs to be surely gripped without breaking or dropping the work, regardless of the physical properties of the work. In recent years, enabling to easily control the grip force of the robot hand is demanded to accurately grip the work in order to realize further advanced product assembly using the industrial robot.
A method of using a disturbance estimation observer to control the grip force of the robot hand (see Japanese Patent Application Laid-Open No. 2002-178281) is proposed as an example of a method of controlling the grip force. To cause a grip apparatus to grip the work in a grip force controlling apparatus disclosed in Japanese Patent Application Laid-Open No. 2002-178281, the driving current and the rotating speed of a motor that provides the grip force are input, and the disturbance estimation observer outputs an estimation value of the grip force of the robot hand. The grip force controlling apparatus disclosed in Japanese Patent Application Laid-Open No. 2002-178281 performs control of eliminating the deviation between the grip force estimation value output from the disturbance estimation observer and a grip force target value to thereby control the grip force of the robot hand.
However, in the invention described in Japanese Patent Application Laid-Open No. 2002-178281, frictional force generated in a driving mechanism that drives fingers is switched from static friction to kinetic friction and is significantly changed in a transition from a state in which the movement speed of the fingers of the robot hand is 0 to a state in which a motor begins to revolve. Therefore, a compensation coefficient of the disturbance estimation observer for estimating the influence of the friction cannot be uniquely identified. In the invention described in Japanese Patent Application Laid-Open No. 2002-178281, hysteresis, i.e. dead zone that cannot be controlled, is provided to the compensation coefficient of the disturbance estimation observer for estimating the influence of the friction when the movement speed of the fingers is 0 and when the movement speed of the fingers is not 0. Therefore, in the invention described in Japanese Patent Application Laid-Open No. 2002-178281, accurate adjustment and control of the grip force of the robot hand is difficult in the state that the robot hand is gripping the work.
A method of using an external force sensor that can measure the grip force and controlling the grip force while measuring the grip force of the robot hand can be considered. However, a member for causing the external force sensor to detect the grip force needs to be separately provided to the robot hand in this case, and downsizing of the robot hand is difficult. Furthermore, the force sensor is generally more expensive than a sensor capable of measuring a position, and reduction in the cost of the robot hand is also difficult. The measurement accuracy of the force sensor is lower than that of a position sensor or the like, and accurate adjustment and control of the grip force of the robot hand is difficult.